1. Field of the Invention
This invention relates to the operation of a reciprocable valve of an internal combustion engine. More particularly, this invention relates to a system for selectively varying the rate at which a valve closes from its fully open position.
2. Description of the Prior Art
As is known in the art, for example, as taught by U.S. Pat. No. 5,002,023 (Butterfield et al.), which is assigned to the assignee of this application and the disclosure of which is incorporated by reference herein, the opening and closing of the reciprocable valves of an internal combustion engine, both the intake valves and the exhaust valves, is customarily actuated by irregularly-shaped cams on a rotating shaft, called a camshaft, whose rotation is effected by a chain or belt drive that connects the camshaft to the engine crankshaft, or to another camshaft in a dual camshaft engine. Typically, each valve is spring-biased against a cam of a camshaft, and its opening and closing cycle is precisely determined by the configuration of the cam against which the valve is spring biased. Occasionally, however, it would be advantageous to engine operation to delay the closing of a valve from a pattern it would otherwise follow if it remained in contact with the cam toward which it is spring biased, and to be able to do so selectively.